1. Field of the Invention
The present invention relates to catheters in general and particularly to cannulas for introducing catheters into a body.
2. Description of the Prior Art
Catheters have a variety of uses especially in the medical field. The term "catheter" is commonly used to identify a tubular instrument that is inserted into various body cavities, either naturally or surgically opened. They can be used for administering fluids into the body, performing blood transfusions, removal of body fluids or components of body fluids, blood pressure determinations, etc.
Conventionally, a catheter is placed into the, body-by any of a number of well known methods. The simplest method is to make a surgical incision in the body and insert the tip of the catheter directly through the incision into the body. Alternatively, a needle is inserted into the body and the catheter is passed through the needle and into the body. The needle is then usually withdrawn leaving the catheter inserted. These methods inevitably involve the loss of blood through the incision. Further, the damage to the skin, blood vessel wall and other body parts makes it difficult to employ the same area when multiple studies are contemplated.
Semi-permanent cannulas are also known. The term "cannula", as it is used here, means a generally tubular device, through which a catheter is placed, which is designed to assist the placement of the catheter in the body. For example, U.S. Pat. No. 4,000,739 to Stevens is directed to a cannula which is adapted to be left in place in the body whether or not a catheter is present. A gasket-like seal having a Y-shaped slit is placed in the cannula in order to prevent any backflow of blood when a catheter is removed. U.S. Pat. No. 4,239,042 to Asai is directed to a catheter placement system which involves a cannula having a body portion and a tip portion. The cannula is useful in avoiding thrombogenic irritations and in avoiding collapse of the catheter during use. However, these patents suffer the disadvantage of being of a relatively large size. Additionally, they are quite bulky to use, often requiring more than one pair of hands for insertion and use.